High-pressure discharge lamp

ABSTRACT

A high-pressure discharge lamp has an outer envelope ( 1 ) in which a discharge vessel ( 11 ) is arranged. The discharge vessel encloses a discharge space ( 13 ) with an ionizable filling. The discharge vessel has two mutually opposed neck-shaped portions ( 2, 3 ) through which current-supply conductors ( 4, 5 ) extend to a pair of electrodes ( 6, 7 ) in the discharge space. A lamp base ( 8 ) of electrically insulating material supports the discharge vessel ( 11 ) via the first and second current-supply conductors. The lamp base is provided with a first ( 14 ) and a second ( 15 ) contact members connected to the respective first and the second current-supply conductor, respectively. The lamp base ( 8 ) and/or the first and/or the second contact member ( 14, 15 ) function as an end-of-life device. Preferably, the lamp base is made from soft glass and the first and the second contact member are made from an oxidized nickel-iron-chromium material, preferably from a NiFeCr alloy such as vacovit.

The invention relates to a high-pressure discharge lamp.

High-pressure discharge lamps ranging from 35 to 150 W have become adominant player in lighting retail applications. Trends have emergedwhich create positive conditions for range extensions towardslower-lumen packages and/or lower wattages. Lower light levels are beingused, for instance in exclusive shops, focusing the light on the goodsinstead of flooding the area. End users in the market become more andmore interested in a uniform quality of the light and would prefer toemploy high-pressure discharge lamps instead of using halogen lamps forthe low-lumen packages and accent lighting.

Generally, high-pressure discharge lamps of the kind mentioned in theopening paragraph either have a discharge vessel with a ceramic wall orhave a quartz glass discharge vessel. Such high-pressure discharge lampsare widely used in practice and combine a high luminous efficacy withfavorable color properties. The discharge vessel of the lamp containsone or several metal halides in addition to Hg and a rare gas filling.

A ceramic wall of a discharge vessel in the present description andclaims is understood to be a wall made from one of the followingmaterials: monocrystalline metal oxide (for example sapphire),translucent densely sintered polycrystalline metal oxide (for exampleAl₂O₃, YAG), and translucent densely sintered polycrystalline metalnitride (for example AlN).

A lamp of the kind mentioned in the opening paragraph is known from theEnglish abstract of JP-A 04 002 035. The known discharge lamp comprisesa discharge vessel and current-supply conductors supporting thedischarge vessel and mounted so as to project from a lamp base of aninsulating material. An outer envelope or outer bulb, of which one endis left open, is fixed to the lamp base and encloses the dischargevessel and the current-supply conductors.

A drawback of the known discharge lamp is that at the end of life (EOL)an increase fill pressure in the lamp allows the occurrence of a glowdischarge. Such a glow discharge can be sustained for an extended periodof time (for example hundreds of hours). This glow discharge may causesputtering of the connection conductor running alongside the dischargevessel resulting in a mirror around the lamp base, which can trigger theso-called incandescent mode, in which the high-pressure discharge lampmay overheat drastically, often exceeding temperatures for the safematerial constraints of the outer envelope and wiring of the dischargelamp.

The invention has for its object to eliminate the above disadvantagewholly or partly. According to the invention, a high-pressure dischargelamp of the kind mentioned in the opening paragraph for this purposecomprises:

an outer envelope in which a discharge vessel is arranged around alongitudinal axis,

the discharge vessel enclosing, in a gastight manner, a discharge spaceprovided with an ionizable filling,

the discharge vessel having a first and a second, mutually opposedneck-shaped portion through which a first and a second current-supplyconductor, respectively, extend to a pair of electrodes arranged in thedischarge space,

a lamp base of electrically insulating material supporting the dischargevessel via the first and second current-supply conductors,

the lamp base being provided with a first and a second contact memberconnected to the respective first and second current-supply conductor,

the lamp base and/or the first and/or the second contact memberfunctioning as an end-of-life device.

According to the invention the lamp base, the first and/or the secondcontact member serve as a fuse in the end-of-life process of thehigh-pressure discharge lamp. The arc discharge between the first andthe second contact member induces stresses in the lamp base. The lampbase starts to melt or to crack under the stresses induced by the arcdischarge. The deterioration of the lamp base prevents the incandescentmodes discussed above.

A preferred embodiment of the high-pressure discharge lamp according tothe invention is characterized in that the lamp base is made from a softglass, hard glass, or ceramic material. Preferably, the lamp base ismade of soft glass. Soft glass has the advantageous property that it hasa low softening point and is comparatively sensitive to thermal shocks.When the incandescent mode occurs, the base made of soft glass willdeform and crack before excessive temperatures are reached.

Preferably, the lamp base is colored whitish, so as to reflect extralight at useful beam angles, which increases the luminous efficacy ofthe lamp effectively. Preferably, the lamp base is in the form of aplate.

A preferred embodiment of the high-pressure discharge lamp according tothe invention is characterized in that the first and the second contactmember are made from a (pre-)oxidized nickel-iron-chromium material.Such a material provides a good thermal match with a base plate made ofsoft glass. Preferably, the first and the second contact member are madefrom a NiFeCr alloy such as vacovit.

A preferred embodiment of the high-pressure discharge lamp according tothe invention is characterized in that the lamp base supports the outerenvelope, and the outer envelope encloses the first and secondcurrent-supply conductors and is connected to the lamp base in agas-tight manner. Controlling of the atmosphere in the outer envelope orouter bulb satisfactorily protects the current-supply conductors againstoxidation. By controlling of the atmosphere in the outer envelope ismeant evacuating of the outer envelope or providing an air-tightenvironment which in particular is free from oxidizing agents such asoxygen. Alternatively, controlling of the atmosphere in the outerenvelope does not exclude that means are provided in the outer envelopeto control the atmosphere in the outer envelope. In an embodiment of theinvention, the outer envelope is filled with nitrogen gas comprising,for example, a small percentage of oxygen. Controlling the oxidation ofthe current-supply conductors makes it possible to position thecurrent-supply conductors relatively close to the discharge vessel.Normally, press seals and/or tipped-off (quartz) tubulations areprovided to reduce oxidation of the current-supply conductors, leadingto a bulky and lengthy high-pressure discharge lamp. For quartzdischarge vessels, the press seal and current-supply conductors arepreferably dimensioned such as to attain the desired life by operationin air. Niobium used in ceramic discharge vessels with niobiumcurrent-supply conductors oxidizes very quickly at the operatingtemperatures of the discharge vessel, leading to a very limited lifespan of the high-pressure discharge lamp.

Preferably, the first and the second contact member issue from the outerenvelope. The first contact member in the lamp base is connected to thefirst current-supply conductor. The second contact member in the lampbase is connected to the second supply conductor via a connectionconductor running alongside the discharge vessel. The first and thesecond contact member provide the mechanical support of the dischargevessel connection and provide the electrical contact between theelectrodes in the discharge vessel and the exterior of the high-pressuredischarge lamp.

The control of the atmosphere in the outer envelope renders it possibleto manufacture a simplified and compact high-pressure discharge lamp. Inparticular, the length of the high-pressure discharge lamp can besignificantly reduced. To this end, a preferred embodiment of thehigh-pressure discharge lamp is characterized in that the ratio of thedistance d_(e) between the electrodes to the height h_(dl) of thehigh-pressure discharge lamp along the longitudinal axis lies in a rangeof: $0.02 \leq \frac{d_{e}}{h_{dl}} \leq {0.2.}$

According to this embodiment of the invention, the height h_(dl) of thehigh-pressure discharge lamp along the longitudinal axis can be smallerthan approximately 50 mm for a distance d_(e) between the electrodesranging from approximately 1 mm to approximately 10 mm.

A preferred embodiment of the high-pressure discharge lamp according tothe invention is characterized in that an exhaust tube for evacuatingthe outer envelope is provided in the lamp base or in the outerenvelope. This has the advantage that the outer envelope can beevacuated via the exhaust tube after the discharge vessel and the outerenvelope have been mounted on the lamp base of the high-pressuredischarge lamp. In a further preferred embodiment, the exhaust tube alsoforms a feed-through element to a current-supply conductor of thedischarge vessel of the lamp. This has the advantage of a simpler lampconstruction.

The lamp base can be manufactured with a high dimensional accuracy. Itis favorable when the lamp base is plane at its surface facing away fromthe discharge vessel. This surface may be mounted against a (lamp)holder, for example a carrier, and accordingly is a suitable surface forserving as a reference for the position of the discharge vessel.

A preferred embodiment of the high-pressure discharge lamp according tothe invention is characterized in that the outer envelope is fastened tothe lamp base by means of an enamel. Preferably, the enamel is providedin the form of a previously shaped ring. Using a previously shaped ringconsiderably simplifies the manufacture of the high-pressure dischargelamp.

The high-pressure discharge lamp according to the invention has theadvantage that, when the lamp is in operation, the discharge vessel hasoptically very compact virtual dimensions, which render the lamp highlysuitable for use in compact luminaires. Because of the specialconstruction of the lamp base of the high-pressure discharge lampaccording to the invention, the discharge lamp is very suitable for usein a reflector. The relatively highly accurate positioning of thedischarge vessel with respect to the base plate and the good dimensionalreproducibility of the base plate allow its use in assemblies withdifferent click-fit connections.

The invention will now be explained in more detail with reference to anumber of embodiments and a drawing, in which:

FIG. 1A diagrammatically shows a high-pressure discharge lamp accordingto the invention;

FIG. 1B a cross-section of the high-pressure discharge lamp as shown inFIG. 1A;

FIG. 2 shows an alternative embodiment of the high-pressure dischargelamp according to the invention;

FIG. 3 shows another alternative embodiment of the high-pressuredischarge lamp according to the invention; and

FIG. 4 shows a further alternative embodiment of the high-pressuredischarge lamp according to the invention.

The Figs. are purely diagrammatic and not drawn true to scale. Somedimensions are particularly strongly exaggerated for reasons of clarity.Equivalent components have been given the same reference numerals asmuch as possible in the Figs.

FIG. 1A shows an artist's impression of a high-pressure discharge lampaccording to the invention. FIG. 1B diagrammatically shows across-section of the high-pressure discharge lamp as shown in FIG. 1A.The high-pressure discharge lamp comprises a discharge vessel 11arranged around a longitudinal axis 22. The discharge vessel 11encloses, in a gastight manner, a discharge space 13 provided with anionizable filling comprising mercury, a metal halide and a rare gas. Inthe example of FIGS. 1A and 1B, the discharge vessel 11 has a firstneck-shaped portion 2 and a second, opposed neck-shaped portion 3,through which portions a first current-supply conductor 4 and a secondcurrent-supply conductor 5, respectively, extend to a pair of electrodes6, 7, which electrodes 6, 7 are arranged in the discharge space 13. Thehigh-pressure discharge lamp is further provided with a lamp base 8 madefrom an electrically insulating material. The lamp base 8 supports thedischarge vessel 11 via the first and second current-supply conductors4, 5. The lamp base 8 also supports an outer bulb or outer envelope 1.In the example of FIGS. 1A and 1B, the lamp base 8 is provided with afirst contact member 14 which is connected to the first current-supplyconductor 4. In addition, the lamp base 8 is provided with a secondcontact member 15 connected to the second supply conductor 5 via aconnection conductor 16 running alongside the discharge vessel 11.

According to the invention, the lamp base 8 and the first and/or thesecond contact member 14, 15 function as an end-of-life device. The lampbase 8 and the first and/or the second contact member 14, 15 serve as afuse in the end-of-life process of the high-pressure discharge lamp. Thearc discharge between the first and the second contact member 14, 15induces stresses in the lamp base 8. The lamp base 8 starts to melt orto crack under the stresses induced by the arc discharge. Thedeterioration of the lamp base 8 prevents the so-called incandescentmodes.

In an alternative embodiment, at least one contact member is formed by afeed-through tube in the lamp base, allowing one of the current-supplyconductors to be fastened in said feed-through tube. Alternatively, twofeed-through tubes may be provided in the lamp base. The fastening inthese feed-through tubes may be done by resistance welding, laserwelding, or crimping. An advantage of the use of feed-through tubesinstead of the contact members is that a greater freedom of positioningof the discharge vessel on the longitudinal axis of the high-pressuredischarge lamp is attained. This may further improve the precisepositioning of the discharge vessel in the outer envelope of thehigh-pressure discharge lamp.

Preferably, the lamp base 8 is provided as a sintered body, preferably asintered ceramic body. Preferably, the lamp base 8 is in the form of aplate. The lamp base 8 can be manufactured with a high dimensionalaccuracy. The lamp base 8 has the additional advantage that it can bemade in a light color, for example white or a pale grey. With the use ofa material having a light color, light emitted by the discharge vessel11 will be reflected at useful beam angles, thereby increasing theefficiency of the luminaire or the total efficiency of the high-pressuredischarge lamp. It is prevented thereby that the light incident on thelamp base 8 is lost to the light beam to be formed by means of areflector. In addition, it is favorable when the lamp base 8 has a flat,planar surface facing away from the discharge vessel 11. This surfacemay be mounted against a (lamp) holder, for example a carrier, forexample a reflector, and accordingly is a suitable surface for servingas a reference for positioning the discharge vessel 11. In anotherfavorable embodiment, the surface of the lamp base 8 facing thedischarge vessel has a central elevation, which serves to center thedischarge vessel 11 and an enamel ring with respect to the lamp base 8during the manufacture of the high-pressure discharge lamp.

Preferably, the outer envelope 1 is connected to the lamp base 8 in agas-tight manner. A control of the atmosphere in the outer envelope 1satisfactorily protects the current-supply conductors 4, 5 againstoxidation. As oxidation of the current-supply conductors 4, 5 isprevented, the current-supply conductors 4, 5 can be positionedrelatively close to the discharge vessel 11. The control of theatmosphere in the outer envelope makes press seals and/or tipped-off(quartz) tabulations redundant, resulting in a simplified and compacthigh-pressure discharge lamp. Preferably, an exhaust tube 18 forevacuating the outer envelope 1 is provided in the lamp base 8. In thismanner, the outer envelope 1 can be evacuated via the exhaust tube 18after the discharge vessel 11 and the outer envelope 1 have been mountedon the lamp base 8 of the high-pressure discharge lamp. After beingevacuated and, if desired, being provided with the desired atmosphereinside the outer envelope 1, the exhaust tube 18 is sealed off.Preferably, a getter is used inside the outer envelope, for example amix of water/hydrogen/oxygen to absorb impurities. It is advantageous ifthe exhaust tube 18 in the lamp base 8 is made from a metal or from aNiFeCr alloy.

Preferably, the outer envelope 1 is made from quartz glass, hard glass,or soft glass. The outer envelope 1 is preferably fastened to the lampbase 8 by means of an enamel of (glass) frit. It is favorable when theenamel is provided in the form of a previously shaped ring. Using such apreviously shaped ring considerably improves the accuracy of positioningof the discharge vessel 11 during the manufacture of the high-pressuredischarge lamp. The choice of the enamel depends on the material of theouter envelope 1 and on the material of the lamp base 8.

In the example of FIGS. 1A and 1B, a substantially cylindrical outerenvelope 1 is provided. FIG. 2 shows an alternative embodiment of thehigh-pressure discharge lamp according to the invention. In the exampleof FIG. 2, a substantially spherical outer envelope 1 is provided.

In the examples of FIGS. 1A, 1B and 2, the discharge vessel 11 is madefrom a ceramic material. In FIG. 2 a sealed exhaust tube 18′ is providedin the outer envelope 1. Providing a glass or quartz tubulation in theouter envelope means that an exhaust tube in the lamp base can bedispensed with. FIG. 3 shows yet another alternative embodiment of thehigh-pressure discharge lamp according to the invention in which thedischarge vessel 11 is made from quartz. In this embodiment theionizable filling in the discharge space comprises mercury, a metalhalide, and a rare gas. In the example of FIG. 3, part of the outerenvelope has a substantially spherical shape. In an alternativeembodiment shown in FIG. 4, the exhaust tube 18 also forms a feedthrough tube to which the current-supply conductor 4 is fastened.

The control of the atmosphere in the outer envelope means that asimplified and compact high-pressure discharge lamp can be made. Inparticular, the length of the high-pressure discharge lamp can besignificantly reduced. To this end, a preferred embodiment of thehigh-pressure discharge lamp is characterized in that the ratio of thedistance d_(e) between the electrodes to the height h_(dl) of thehigh-pressure discharge lamp along the longitudinal axis lies in a rangeof: $0.02 \leq \frac{d_{e}}{h_{dl}} \leq {0.2.}$

According to the invention, a simplified lamp design is provided whichcan be used as a building block for a family of products based on amodular capsule lamp. The discharge vessel 11 is supported on thecurrent-supply conductors 4, 5 that are fixedly connected to the baseplate 8. The discharge vessel 11 as well as the current-supplyconductors 4, 5 are positioned in the outer envelope 1, which is keptunder a controlled atmosphere. Elimination of the press seals and and/ortipped-off (quartz) tubulations results in a compact high-pressuredischarge lamp. Preferably, the height h_(dl) of the high-pressuredischarge lamp is equal to or less than 50 mm, preferably less than 40mm. In addition, positioning issues of the discharge vessel 11 areeliminated owing to the more controlled manufacture of the high-pressuredischarge lamp with respect to the longitudinal axis 22 and, inaddition, the discharge vessel 11 can be accurately positioned in aplane orthogonal to the longitudinal axis 22.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.Use of the verb “comprise” and its conjugations does not exclude thepresence of elements or steps other than those stated in a claim. Thearticle “a” or “an” preceding an element does not exclude the presenceof a plurality of such elements. The invention may be implemented bymeans of hardware comprising several distinct elements, and by means ofa suitably programmed computer. In a device claim enumerating severalmeans, several of these means may be embodied by one and the same itemof hardware. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage.

1. A high-pressure discharge lamp comprising: an outer envelope (1) inwhich a discharge vessel (11) is arranged around a longitudinal axis(22), the discharge vessel (11) enclosing, in a gastight manner, adischarge space (13) provided with an ionizable filling, the dischargevessel (11) having a first (2) and a second (3) mutually opposedneck-shaped portion through which a first (4) and a second (5)current-supply conductor, respectively, extend to a pair of electrodes(6, 7) arranged in the discharge space (13), a lamp base (8) ofelectrically insulating material supporting the discharge vessel (11)via the first and second current-supply conductors (4, 5), the lamp base(8) being provided with a first (14) and a second (15) contact memberconnected to the respective first and second current-supply conductor(4, 5), the lamp base (8), and or the first and/or the second contactmember (14, 15) functioning as an end-of-life device.
 2. A high-pressuredischarge lamp as claimed in claim 1, characterized in that the lampbase (8) is made from a soft glass, hard glass, or ceramic material. 3.A high-pressure discharge lamp as claimed in claim 1, characterized inthat the first and the second contact member (14, 15) are made from anoxidized nickel-iron-chromium material.
 4. A high-pressure dischargelamp as claimed in claim 3, characterized in that the first and thesecond contact member (14, 15) are made from a NiFeCr alloy.
 5. Ahigh-pressure discharge lamp as claimed in claim 1, characterized inthat the lamp base (8) supports the outer envelope (1), the outerenvelope (1) encloses the first and second current-supply conductors (4,5), and the outer envelope (1) is connected to the lamp base (8) in agas-tight manner.
 6. A high-pressure discharge lamp as claimed in claim5, characterized in that the first and the second contact member (14,15) issue from the outer envelope (1).
 7. A high-pressure discharge lampas claimed in claim 1, characterized in that an exhaust tube (18, 18′)for evacuating the outer envelope (1) is provided in the lamp base (8)or in the outer envelope (1).
 8. A high-pressure discharge lamp asclaimed in claim 7, characterized in that the exhaust tube (18) in thelamp base (8) is made from a metal or from a NiFeCr alloy.
 9. Ahigh-pressure discharge lamp as claimed in claim 1, characterized inthat the ratio of the distance d_(e) between the electrodes (6, 7) tothe height h_(dl) of the high-pressure discharge lamp along thelongitudinal axis (22) lies in a range of:$0.02 \leq \frac{d_{e}}{h_{dl}} \leq {0.2.}$